Shop Talk with Trent Wallman
"Is It Getting Looked At
December 1, 2020
We have recently purchased a couple new to us 152’s, and with that always comes a long list of squawks to take care of. We always treat a new plane to an annual inspection where we will also upgrade and replace old equipment. Just about every time I annual a new to us plane, I find things that have been looked over, neglected, or straight up pencil whipped. I understand not everything can be made perfect on an airplane. Nobody has the time or money for that. Items that don’t have an immediate impact on safety tend to get neglected. Unfortunately, some of those neglected items can build into safety issues. I would like to talk about a few of these items I have seen being overlooked out in the field. Take these items with you to your next inspection and ask your mechanic about them. I love when an owner asks me about their plane, and I look forward to sharing the details of what we find with them. These are pretty basic items that should routinely be done/checked at annual, and any mechanic doing his due diligence will be happy to talk with you about them.
Wheels and brakes tend to not get the attention they deserve. Sure, you only need them for a short time, but that short time you need them can become exciting very quickly if they fail you. We often find brake linings and discs worn too thin, wheel bearings with old grease in them, and worn out wheel half mounting hardware. You have to take the wheel half apart to change the tire and tube. I am amazed at the rusty hardware and or worn out self locking nuts I find people reusing. These parts are cheap and replacing them is easy. If your wheels hardware is looking rusted or worn, consider asking for replacements at the next tire change. Removing, cleaning, inspecting, greasing, and reinstalling wheel bearings is part of a normal annual inspection. Ask what your bearing races looked like and what kind of grease was used to service those bearings. That is an easy way to know if your wheels are being looked over as they should be. Looking at the wheels axle nut is another clear tell on weather or not the wheel has been off and looked at. If the axle nut is caked in dirt and has an old not shiney cotter pin in it, your wheel was given the “good enough” treatment.
The biggest safety issue I find being overlooked is flight control rigging. Flight control rigging seems to often get the “good enough” treatment, and I understand why. Control rigging and cable tensioning can be a difficult and annoying job sometimes. However, I personally don’t want my controls to be good enough. I want my controls to respond exactly the way they were designed to, so I can fly and or recover the way the aircraft has been certified to do so. An annual inspection includes checking flight control cable tension and overall travel. Often, someone will just move the control surface through its full travel, feel it hit some sort of stops, pluck the cable, and call it good enough. Aircraft maintenance manuals have published travel ranges in degrees and cable tension in pounds. At your next annual, ask the mechanic to see the manufacturers published tolerances, and ask to see what was found on your aircraft. If that information isn’t recorded anywhere on an inspection report or in any notes, you know you got the “good enough” treatment. This can also happen with engine control rigging. I’ve seen a lot of carb and carb heat cables rigged with that same attitude.
Magneto timing is another item that is easy to check in on. This is another routine inspection item that I find people allowing to drift. I have looked at planes just coming out of other inspections with timing five degrees off. Engines will still make power with timing that far off. Due to a magneto install mishap I observed, I learned that the engine will still run with timing off as much as 30 degrees. The engine couldn’t make more than 1500 RPM, but amazingly, it still ran smoothly. The data plate on your engine gives you the exact spark advance the magnetos need to be set to. Tolerance is plus or minus one degree, and it’s half of a degree for turbo charged/normalized engines. It’s normal for the timing to drift as the points/cam wear inside the magneto. Bumping the mag to reset the timing can be done a couple times, but if timing continues to drift, I’d recommend looking into the magneto point assembly/cam. As the mag parts wear and external engine timing continues to drift, the magnetos internal timing will also drift and the spark it produces will weaken. Most people seem to already ask about engine cylinder compressions. Next time, also ask what the magneto timing was found to be at.
These are just a few things to think and talk about in regards to the stewardship of your aircraft. I encourage everyone to be involved in the inspection process and ask questions. The power of knowledge brings an element of safety and a sense of confidence in the operation of your aircraft. Here’s to blue skies and smooth engines!